In recent years, e-mails have been frequently used through a communication terminal such as a computer or a mobile phone. As the use of e-mails increases, spam mails have become a concern, which are a large number of junk e-mails sent to a large number of recipients without the recipients' consent. Therefore, anti-spam systems have been used that are capable of detecting spam mails so that users can efficiently receive only the e-mails they need.
FIG. 14 illustrates a first conventional anti-spam system 10. An anti-spam system 10 includes a managing center 12 that manages the information regarding spam mails; an e-mail system 16 that detects a spam mail from a received e-mail 14 and processes it based on the information managed by the managing center 12; and user PCs 18 that receive the e-mail 14 except the spam mail, through the e-mail system 16.
The managing center 12 is coupled to the e-mail system 16 via a network or a communication line. The e-mail system 16 is capable of receiving the e-mail 14 from an external apparatus through a network. The e-mail system 16 may be, for example, an internet service provider (ISP), which offers internet services, or a network system such as a server installed in a company.
The managing center 12 manages the information regarding spam mails, for example, by creating a database 22 based on a large number of spam mails collected in a spam collecting system 20 such as a honeypot. The honeypot may collect unsolicited e-mails, i.e., spam mails by creating an e-mail address for a fictitious person, for example. The information regarding a newer spam mail is added to the database 22 each time the spam mail is found. Therefore, the volume of the information to be stored therein increases as time elapses.
A gateway 30 disposed in the e-mail system 16 downloads the database 22 from the managing center 12 at predetermined intervals. Based on the database 22, a determining portion 32 determines whether the received e-mail 14 is a spam mail. As described above, the gateway 30 is capable of detecting spam mails. Legitimate e-mails 14 other than spam mails pass through the gateway 30, and are stored in a mail server 36, and delivered to each of user PCs 18a-18c in accordance with a request from the user PCs 18.
FIG. 15 illustrates a second conventional anti-spam system 50. In a second anti-spam system 50, the determination of whether an e-mail is a spam mail can be done in a managing center 12. A mail information extracting portion 34 in a gateway 30 extracts the information regarding a received e-mail 14, and transmits the extracted information, which is called signature, to a determining portion 24 in the managing center 12. Based on the received signature and a database 22, the determining portion 24 determines whether the received e-mail 14 is a spam mail, and transmits the result of the determination to the gateway 30. Based on the received result of the determination, the gateway 30 is capable of detecting spam mails. U.S. Pat. No. 6,330,590 discloses a technique used for the second anti-spam system 50.